Idle speed control using alternator

ABSTRACT

An engine system includes an engine, an alternator, a load, and a controller that communicates with the engine, the alternator, and the load. The controller signals the engine to drive the alternator when the engine idles. When a load increase on the engine is detected, the controller reduces an alternator load on the engine in response to the load increase. Air flow into the engine is adjusted to compensate for the load increase, and concurrently the alternator load is increased. When a load decrease is detected, the alternator load is increased, and the air flow is subsequently adjusted while decreasing the alternator load. In another embodiment, spark timing of the engine is adjusted to compensate for the load decrease.

FIELD OF THE INVENTION

The present invention relates to engine idle speed control, and moreparticularly to using an alternator to achieve engine idle speedcontrol.

BACKGROUND OF THE INVENTION

Vehicle engines provide power for a plurality of external loads such asan alternator, an A/C compressor, a power steering pump, a hydraulicpump, etc. When these loads require power, the engine, increases poweroutput to maintain driving power, which is noticeable when the engine isidling. A noticeable dip in engine idle speed occurs when engine poweris used to drive the load, which is undesirable.

Conventional engine controllers advance the spark timing of the engineto compensate for the loss in engine power and the resulting dip in idlespeed. Spark advance provides a fast acting engine torque actuator thatcompensates for the reduced engine power and maintains constant speed.During idle, spark advance causes the engine to be less efficient.Additionally, combustion instabilities occur and difficulties arepresented in misfire calibration.

SUMMARY OF THE INVENTION

The present invention provides an engine system having an engine, analternator, a load, and a controller. The controller communicates withthe engine, the alternator, and the load. The controller signals theengine to drive the alternator when the engine idles. When thecontroller detects a load increase on the engine, the controller reducesa load of the alternator on the engine to maintain an idle speed of theengine.

In one aspect, the controller adjusts air flow into the engine tocompensate for the load increase and concurrently increases thealternator load.

In another aspect when the controller detects a load decrease on theengine, the controller increases the alternator load to compensate forthe load decrease. Further, the controller adjusts the air flow into theengine while decreasing the alternator load to maintain the idle speedof the engine.

In an alternative aspect, when the controller detects a load decrease onthe engine, the controller adjusts spark timing of the engine tocompensate for the load decrease to maintain the idle speed of theengine.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an engine system;

FIG. 2 is a flowchart detailing an engine idle speed control methodaccording to the present invention; and

FIG. 3 is a graph detailing the engine idle speed control method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. For purposes of clarity, the same referencenumbers will be used in the drawings to identify similar elements.

With reference to FIG. 1, a block diagram of an engine system 10according to the present invention is shown. The engine system 10includes an engine 12 and an intake manifold 14. Air is directed intothe cylinders (not shown) of the engine 12 through the intake manifold14. A throttle 18 controls the mass of air flowing to the intakemanifold 14. The throttle 18 can be adjusted directly by an acceleratorpedal or by an electronic throttle controller and the accelerator pedal.

An alternator 20 is selectively driven by the engine 12 to charge abattery 22. The engine 12 provides power to one or more loads 24. Theload 24 represents one or more engine-driven loads including, but notlimited to, an air conditioning compressor, a power steering pump,transmission pump, and the like. A controller 26 communicates with thethrottle 18, the engine 12, the alternator 20, and the load 24. Thecontroller 26 executes an engine idle speed control algorithm, as willbe discussed in further detail below.

Referring now to FIG. 2, the idle speed control algorithm will bediscussed in detail. After a start step, control determines whether anidle condition of the engine 12 is detected in step 100. If an idlecondition is not detected, control loops back to step 100. If an idlecondition is detected, control signals an increase in the alternatorload on the engine 12 in step 102. In step 104, the engine 12 operatesat the increased alternator load.

In step 106, control checks whether the idle condition is still present.If not, control operates the alternator 20 at a standard load in step108 and controls ends. The standard load reflects the load required tomaintain a charge level of the battery 22. The standard load isdetermined by a conventional battery charge algorithm. If the idlecondition is still present, control determines whether there is anincreased load on the engine 12 in step 110. An increased load on theengine 12 occurs when the load 24 is driven by the engine 12. If thereis no load increase on the engine 12, control continues with step 112.If there is an increased load on the engine 12, control continues withstep 114 where the alternator load is decreased to compensate for theload increase.

After decreasing the alternator load, the air intake into the engine 12,and the alternator load are increased in steps 116 and 118,respectively. The increased air intake increases the engine idle speed.The concurrent increase in alternator load, which would otherwisedecrease the engine idle speed, maintains the engine idle speed at asubstantially constant value. Gradually, the alternator load isincreased to the level prior to the decrease in step 114. After steps116 and 118 have been executed, control loops back to step 104.

In step 112, the algorithm determines whether there is a load decreaseon the engine 12. If there is no load decrease, control loops back tostep 104. If a load decrease is detected, control continues with step120, where, in accordance with one embodiment of the present invention,the alternator load is increased. In this manner, the alternator loadcompensates for the decreased load, and maintains engine idle speed.Once the alternator load has been increased, the air intake into theengine is decreased, and the alternator load is decreased in steps 122and 124, respectively. The decreased air intake decreases the engineidle speed. The concurrent decrease in alternator load, which wouldotherwise increase the engine idle speed, enables the engine idle speedto remain constant.

With reference to step 120, and in accordance with an alternativeembodiment, if a load decrease is detected, spark timing of the engine12 is adjusted to compensate for the decreased load to maintain theengine idle speed.

FIG. 3 depicts the engine idle speed, air intake, alternator load, andaccessory load as a function of time. As shown, the engine idle speedremains static until time t₁, when the load 24 is switched on. Inresponse to activation of the load 24, the alternator load immediatelydecreases, and compensates for the load 24. Between times t₁ and t₂, theair intake and alternator load are increased until the alternator loadachieves the prior (pre-t₁) level. The engine idle speed remains static.At time t₃, the load 24 is turned off and the alternator loadimmediately increases to compensate for the decreased load. Betweentimes t₃ and t₄, the air intake is decreased and the alternator loaddecreases, until the alternator load achieves its pre-t₃ level. As aresult, the engine idle speed remains constant.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the present invention can beimplemented in a variety of forms. Therefore, while this invention hasbeen described in connection with particular examples thereof, the truescope of the invention should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, the specification and the following claims.

1. An engine system comprising: an engine; an alternator having anadjustable load driven by said engine; a second load that is selectivelydriven by said engine; and a controller that communicates with saidengine, said alternator, and said second load, wherein said controllersignals said engine to drive said alternator when an idle condition isdetected, and wherein when said controller detects an increase in saidsecond load on said engine, said controller reduces said adjustable loadof said alternator on said engine in response to said increase in saidsecond load while adjusting spark timing to maintain an idle speed ofsaid engine.
 2. The engine system of claim 1 wherein said controlleradjusts air flow into said engine to compensate for said second loadincrease and concurrently increases said adjustable load.
 3. The enginesystem of claim 2 wherein said controller detects a decrease in saidsecond load, increases said adjustable load to compensate for saidsecond load decrease, and adjusts said air flow into said engine whiledecreasing said adjustable load to maintain said idle speed of saidengine.
 4. A method of controlling idle speed of an engine comprising:operating an alternator to provide an alternator load when an idlecondition is detected; detecting a load increase on said engine; andreducing said alternator load on said engine in response to said loadincrease to maintain said idle speed of said engine.
 5. The method ofclaim 4 further comprising: adjusting air flow into said engine tocompensate for said load increase; and increasing said alternator loadconcurrently with said adjusting.
 6. The method of claim 4 furthercomprising: detecting a load decrease on said engine; and adjustingspark timing to compensate for said load decrease, to maintain said idlespeed of said engine.
 7. The method of claim 5 further comprising:detecting a load decrease on said engine; increasing said alternatorload to compensate for said load decrease; and adjusting said air flowinto said engine while decreasing said alternator load to maintain saididle speed of said engine.
 8. A method of controlling idle speed of anengine comprising: detecting an idle condition of said engine;increasing an alternator load in response to said idle condition;detecting a load increase on said engine; and reducing said alternatorload on said engine in response to said load increase to maintain saididle speed of said engine.
 9. The method of claim 8 further comprising:adjusting air flow into the engine to compensate for said load increase;and increasing said alternator load concurrently with said step ofadjusting.
 10. The method of claim 8 further comprising: detecting aload decrease on said engine; and adjusting spark timing to compensatefor said load decrease, to maintain said idle speed of said engine. 11.The method of claim 9 further comprising: detecting a load decrease ofsaid engine; increasing said alternator load to compensate for said loaddecrease; and adjusting said air flow into said engine while decreasingsaid alternator load to maintain the idle speed of said engine.
 12. Amethod of controlling idle speed of a spark ignition engine comprising:detecting an idle condition of an engine; increasing an alternator loadin response to said idle condition; and reducing said alternator load inresponse to a load increase on said engine to maintain an idle speed ofsaid engine.
 13. The method of claim 12 further comprising: detectingsaid load increase on said engine; adjusting air flow into the engine tocompensate for said load increase; and increasing said alternator loadconcurrently with said adjusting.
 14. The method of claim 13 furthercomprising: detecting a load decrease on said engine; increasing saidalternator load to compensate for said load decrease; and adjusting saidair flow into said engine with an electronic throttle while decreasingsaid alternator load to maintain said idle speed of said engine.
 15. Themethod of claim 13 further comprising: detecting a load decrease on saidengine; and adjusting spark timing to compensate for said load decreaseto maintain said idle speed of said engine.